SPL TwinTube, Руководство пользователя

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Analog Elemental Series
Premium Mic Pre | Control Elements
About Leveling
Initially you should always deactivate the -10 dB button to have correct values displayed by the
VU meter (see “-10 dB” below). Now turn up the Mic Gain control until the VU meter displays
maximum levels between 0 dB and +3 dB. At this level you don’t risk any overdrive when you
experience sudden and unexpected peaks in the level of the source. Always remember that
the VU meter only shows average values and that a peak level can be much higher (up to
+10 dB). If necessary, turn on the PPM mode to see the actual peak levels.
Usually levels of around 0 dB and +3 dB are safe. If, however, you experience very high peaks
already at minimum Mic Gain values (i.e. drums, brass instruments), you can activate the
PAD function (see “PAD” on page 18). The input level is now reduced so that you can regulate
Mic Gain again in a useful range.
If you know in advance that the level will be very consistent you can always turn up Mic Gain.
In this case you can activate the -10dB button to have more headroom in the display.
VU Meter
The VU meter displays the output level of the preamp. The gauge indicates levels from -20 dB
to +5 dB. If necessary you can lower the sensitivity by 10 dB so that the gauge goes up to
+15 dB output level (see “-10dB” below and “About Leveling” above).
The VU meter is custom made to meet SPL specifications and assures a balanced optical
perception thanks to it’s optimized ballistics.
An especially interesting feature is the option to switch between two display modes: VU mode
and PPM mode. The VU mode (VU=Volume Unit) displays average levels, thus provides infor-
mation on the overall loudness. The PPM mode (PPM=Peak Program Meter) displays the peak
levels.
The integration time of the display complies with the BBC requirements. In VU mode the rise
time up to 0 dB is approx. 300 ms. In PPM mode the rise time up to 0 dB is about 2 ms and the
release time down to -20 dB is at a “slow” 1,5 seconds. This calibration ensures to display even
short peaks up to about +6 dB since the needle does not have to travel the entire distance of
the gauge every time.
PPM
The PPM button allows to switch the VU metering characteristics from VU display mode
(button is deactivated and not illuminated) to PPM display mode (button is active and illumi-
nated). A/D converter display also make use of the PPM mode. Monitoring peak levels is most
important to avoid overloading the converter and to prevent audible distortion. Peak levels
are always above the average levels. It may make sense in most cases to also press the -10 dB
button to prevent the needle from getting stuck on the right side of the gauge.
-10
With this button you can change the sensitivity of the VU display. If you press the -10 dB button
(button is illuminated), the sensitivity of the display is lowered by 10 dB. With the needle for
example at 0dB, a value of +10 dB is displayed. Now you can read values of up to +15 dB.
You always have to add these 10 dB to the displayed values, for example if you compare these
values with those of an A/D converter. Remember that A/D converters show peak levels, not
average levels. For comparison press the PPM button to activate the PPM mode.
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